PROVO, Utah – Cody Vaz insists he isn't nervous, even if the hopes of No. 10 Oregon State ride on him, a quarterback who hasn't started a game since he was in high school.

"We're going to go win the game with Cody," Beavers coach Mike Riley said of the junior, who steps in for the injured Sean Mannion when Oregon State visits BYU on Saturday. "Cody's a good quarterback and he's been preparing for this for a long time. He'll be good and we'll be ready to go."

Brigham Young has other plans, even if it, too, is dealing with quarterback issues.

The Cougars (4-2) are expected to start senior Riley Nelson, back after missing the previous two games with what he said were "back fractures." While BYU coach Bronco Mendenhall said Nelson was on track to start this week anyway, there wasn't much choice after talented freshman Taysom Hill tore up his left knee last week on his 19th carry when he should have been taking a knee.

Two quarterbacks in the spotlight, one aiming to continue a passing attack that ranks eighth in the nation, and the other looking to quiet critics who question his health, ability and aggressive running style.

"We know Cody's going to come in and do his job," Oregon State cornerback Rashaad Reynolds said. "Obviously, he's here for a reason."

Nelson is also, opening as BYU's fiery leader only to see his run end with a series of turnovers in a 7-6 loss to No. 24 Boise State on Sept. 20.

Some still question if he will play, a notion Nelson laughs off.

"I'm playing," said Nelson. "There's no espionage going on. I've taken every rep, every snap and I am playing 100 percent."

BYU has proven it can win without much offense, thanks to a defense ranked fifth nationally, 12th against the pass and first against the run, having not allowed an opposing offense to score in 13 consecutive quarters.

"It's going to be a tough, physical game," Riley said. "We know BYU pretty well and you've got to match their physicalness all the way around, both sides of the ball. It's a big, big challenge on both sides of the ball."

Last year, BYU went to Corvallis and beat the Beavers 38-28, with Nelson passing for 217 yards and three touchdowns and rushing for 87 yards. The Cougars also snapped Oregon State's five-game bowl win streak with a 44-20 victory in the 2009 Las Vegas Bowl.

This is an improved Beavers team, aiming for their first 5-0 start since 1939. The No. 10 ranking is Oregon State's highest since 2001.

While they may not have Mannion, who was averaging 339.5 yards passing a game, the Beavers still have his talented receiving duo in Markus Wheaton (124.5 yards a game) and Brandin Cooks (121.5).

"Their offense is their offense," said Mendenhall, who isn't expecting drastic changes in one week. "They have good players all around (Vaz) and their comments as coaches are they have confidence in him, he's a quick decision-maker and a good leader. So my guess is they'll be similar and we'll have to adjust if they're not."

Oregon State's defense is no pushover, ranked first nationally in opponents' third-down conversions, fourth nationally against the run but only 106th against the pass.

"They are very good and physical and play hard and disciplined," Nelson said. "I'm glad we got to play Utah State (a 6-3 win last week) because they played very sound. Oregon State will be similar, not in scheme but as far as being disciplined. It's going to be a grind, and hopefully we can sustain drives and when we do get in the red zone, score touchdowns."

The stage certainly will be different from what Vaz experienced at St. Mary's High School in Stockton, Calif., where he last started.

"I'm not really nervous, more so excited," Vaz said. "It's a great opportunity for our team. We're going into a tough place to play, a really good football team, a really good defensive team. It will be a great opportunity for us."

A sellout crowd of more than 63,000 is expected for homecoming Saturday afternoon and BYU's Heisman Trophy winner Ty Detmer will be honored by the College Football Hall of Fame.

Plus, for the first time in the modern era, BYU will don all-black uniforms rather than its traditional blue-and-white.

"It will still be formidable no matter who is playing quarterback for them," Mendenhall said. "They're a good team. That's why they're voted 10th. They're undefeated and it's not easy to do that. They'll be good enough."

Mendenhall has his own history with Oregon State.

He was their team captain in 1987, and started at safety the last time the Beavers came to Provo in 1986.

When Oregon State pulled off the 10-7 upset win over BYU 26 years ago, Mendenhall celebrated by laying spread eagle at the 50-yard line.

At the time it was special because his dad had played at BYU and his older brother as well.

"I remember that game and it was fun," he said. "This game isn't any more significant because I (went) there. It's just a really good team coming in."